I have fed BOSS and ground flax and worked at a barn that fed them as well. I did not notice much of a difference in the horses coats when fed both. There were a lot of sunflowers growing in the pastures, however :)
A vet technician friend told me flax was considered a "hot" addition, much like cracked corn was believed to make a horse "hot." I did not see it affect any horses except for my own in that manner. Mine were Morgans the others were thoroughbreds, so I am not sure if breed had anything to do with it.
I have fed BOSS off and on over the years depending on price. The horses love it. They had good coats regardless and I never noticed any difference with the arthritic ones, but I was just feeding a big handful as a bedtime treat. Did have a pretty manure pile from the spillage, and the birds appreciated the food source from the random sunflowers. You don't feed the striped ones because the hulls are coarser/less digestable and have been implicated in impaction colics.
I would be interested to see any actual data on how much you would have to feed for benefits and how much before the omega balance has a negative affect.
has there actually been any research to show what the equine needs/ratios of omega 3:6 are? Last I read there hadn't been any studies for that.
I haven't seen any scientific studies on it either, but usually see it compared to the ratio in fresh grass. This SmartPak article lists the ratios in some of the more common feeds: The Truth about Feeding Horses Corn Oil » SmartPak Equine Blog (Fresh grass is listed at 5:1 omega-3 to omega-6) They don't list how much omega-3 or -6 is in there, though- just the ratio between the two.
My mare loves her sunflower seeds! She's kind of picky about her treats, lol, and this is one she loves. I used to feed them about a 1/2 cup a day when they were at home and they had beautiful shiny coats. She's boarded somewhere else now, so she only gets some when I go out more as a treat now. I have noticed that her coat doesn't seems as shiny and sleek as it did before, but it could be other factors.